battery charge on Merlins

About a year ago I upgraded to the 230mah batteries from the 200mah's in my SBAM. Previously, with the 200mah batteries I could get up to aprox. 8 hours listening time in pure battery mode (PC unplugged). With the 230mah's I only get aprox. 5 1/2 hours listening time before distortion sets in.

Is this normal, and how many hours do you get in pure battery mode? Also, I assume loudness is a factor in charge time.

Also,I assume these batteries are getting a full charge, ie. no memory issues. I periodically unplug the SBAM for at least 24 hours to fully drain the batteries. I've also had this same charge time for the past year, no change from when batteries were new.

Thanks, Scott